Jökull - 01.01.2020, Page 14

Glacier extent in Iceland, 1890–2019
tungnajökull, except Öræfajökull for which the aerial
images have been scanned and re-processed) is based
on the AMS maps with some corrections; by georef-
erencing the scanned maps individually, and fitting
each map segment to the surrounding valley walls, us-
ing lidar DEMs as reference topography (for more de-
tails see Pálsson et al., 2012, and Hannesdóttir et al.,
2015b).
Glacier extent in 1970–1980
Glacier outlines for the decade 1970–1980 have been
digitized from early Landsat 1 (previously known as
ERTS-1) images acquired in the summer of 1973,
with a Ground Sampling Distance (GSD) 60×60 m
and aerial images from the National Land Survey of
Iceland from the 1970s (with a GSD of 0.7×0.7 m).
The aerial images have been processed for creation of
orthoimages and DEMs, and they were used to create
additional glacier outlines in areas not covered by the
1973 Landsat imagery, and improve outlines in a few
areas. This includes glacier margins for the smaller
ice caps and glaciers (see Table 2 for details). The
outlines of a few glaciers are based on declassified
Hexagon KH9 satellite images aquired in 1980 (Be-
lart et al., 2019, 2020).
Glacier extent in ∼2000
Multiple imagery sources were used to delineate the
glacier margin for ∼2000. These included orthorecti-
fied aerial images from the company Loftmyndir ehf.
(GSD of 1×1 m), satellite images from both Landsat 7
(GSD of 15×15 m) and SPOT-5 (GSD of 2.5×2.5 m
and 5×5 m) and georeferenced oblique images taken
from an airplane. The year of acquisition varies be-
tween sources from 1998 to 2004. The orthoimages
(airborne and spaceborne) also have different GSD.
For information relating to each glacier or glacierized
area see Table 2.
Glacier extent in 2007–2013
During 2008–2012, starting during the International
Polar Year, accurate and detailed DEMs of the
glaciers in Iceland were produced with airborne li-
dar. The lidar DEMs have a GSD of 5×5 m and
hillshades were created from them for delineation
of glacier outlines (Jóhannesson et al., 2011, 2013).
More than 90% of the glaciers were surveyed in this
effort, including Vatnajökull, Hofsjökull, Mýrdalsjök-
ull, Drangajökull, Eyjafjallajökull and several smaller
glaciers. Approximately 70% of Langjökull was sur-
veyed by the Scott Polar Research Institute (SPRI) in
late summer 2007, and almost the whole glacier again
in 2013, including Þórisjökull (Pope et al., 2013).
Hofsjökull was also resurveyed by lidar in 2013. The
lidar mapping generally includes a 500–1000 m wide
ice-free buffer zone around the ice margins which
contains many glacial geomorphological features, and
therefore the new DEMs have proved to be useful in
geological investigations of proglacial areas.
Glacier extent in 2014
Glacier outlines of 2014 based on aerial images from
Loftmyndir ehf. and Landsat 8 satellite images are
part of the glacier inventory presented here and sub-
mitted to GLIMS. Many of the smaller glaciers, par-
ticularly on Tröllaskagi, were snow-covered in late
summer in 2014, and the glacier margin is hard to
delineate in some areas for this reason. The outlines
from 2014 are not shown on the maps in this paper for
clarity because they are hard to distinguish from the
outlines from ∼2010 and 2019. Data from 2014 are,
however, included in the time series of glacier area
shown in the Results section.
Glacier extent in 2017
During the summer and autumn of 2017, Sentinel-2
satellites acquired images (GSD of 10×10 m) of all
the major glaciers in Iceland. To fill in the missing
patches a mix of Landsat 8 and orthorectified aerial
images from the company Loftmyndir ehf. were used.
Kääb et al. (2016) noted lateral offsets in the geolo-
cation of Sentinel-2 data. We found this offset to
be quite small for the Icelandic glaciers and it is ne-
glected here for simplicity since it does not affect cal-
culations of glacier area. The outlines from 2017 are
not shown on the maps in this paper for clarity be-
cause they are hard to distinguish from the outlines
from ∼2010 and 2019.
Glacier extent in 2019
During the summer and autumn of 2019, Sentinel-2
satellites acquired images (GSD of 10×10 m) of all
JÖKULL No. 70, 2020 11